Perovskitas do tipo LaNixCo1-xO3 suportadas em SBA-15 como precursores de catalisadores Ni-Co aplicados à reforma a vapor do etanol
Resumo
The production of hydrogen from the steam reforming process of ethanol stands out as
a process for the diversification of the world energy matrix, which aims to reduce environmental
impacts and ensure energy security. Among the catalysts already evaluated for this process,
those based on metals such as Ni and Co are active for the reaction, but can be deactivated by
the formation of carbon on the surface and sintering of the metal particles. Among the strategies
to increase the performance and stability of these catalysts, the synthesis from perovskite
precursors (ABO3) makes it possible to obtain metals (B) highly dispersed in oxides (AOx).
However, the compounds obtained from these structures have low surface area, which decreases
the active surface of the material. To study the effects of the nature and composition of the
catalysts and the increase of the specific area, Ni, Co and Ni-Co catalysts obtained from
LaNixCo1-xO3 and LaNixCo1-xO3/SBA-15 perovskites were prepared and applied to the reform
to the ethanol vapor. In order to define a synthesis method for the formation of perovskites on
the mesoporous support SBA-15, the precursor materials were synthesized from impregnations
based on the modified Pechini and amorphous citrate methods. The synthesis of perovskites on
SBA-15 from impregnation based on the modified Pechini method showed less tendency to
form secondary phases. The Ni catalyst obtained from the reduction of this material presented
higher activity and yield for H2 production when compared to that obtained by the amorphous
citrate method. From this method, materials with different proportions of perovskite on the
support and mass perovskites were prepared. The increase of the perovskite ratio on the support
indicated a higher formation of segregated NiO and less dispersion of the active phase. The
catalytic activity and the rate of carbon formation, however, were similar among the materials,
even in view of the increase in the metallic percentage. The introduction of Co into the B site
of the perovskite structure leads to the reduction of the formation of secondary phases, due to
the higher stability, that perovskite with the insertion of this cation in its crystalline lattice
happens to present. The catalysts with Ni-Co and Co showed lower activity for the reaction, but
the rate of carbon formation decreased, due to the lower Co activity in the C-C bond breakage
and its greater ability to activate the water. Comparison of the performance of the supported
catalysts with those synthesized from the perovskite masses showed increased catalytic activity
and reduced carbon formation in the materials supported in SBA-15, due to the greater
dispersion of the active phase.